When automobile automatic transmissions are repaired, the torque converter is usually disassembled, inspected and rebuilt. Generally, most of the key components are reusable. Worn and damaged parts are replaced as needed. Some original equipment (OE) torque converters are difficult to rebuild, often because the OE construction was optimized for high production rather than ease of repair. Specialized equipment is often required to repair OE torque converters, or rebuilders may simply refuse to repair certain models due to excess cost and complexity associated with repair versus replacement.
FIG. 1 is an exploded view of a portion of a prior art OE torque converter 100. The illustrated example is a torque converter from Ford's model number 6R140 transmission, which has been sold in large volumes for several years and is used in some relatively high cost diesel trucks. As described more below, prior art OE torque converter 100 has some common failure modes that are difficult to repair.
Torque converter 100 includes a cover 102 and lock-up clutch assembly 104; the lock-up clutch assembly including a piston 106 that is configured to engage a clutch pack 108 against a backing ring 110 to engage the lock-up clutch assembly. Clutch pack 108 includes two metal clutch plates 112, including front metal clutch plate 112F and rear metal clutch plate 112R, and a friction clutch plate 114 positioned therebetween. Metal clutch plates 112 each include a plurality of outer teeth 116 (only one labeled on each) that are sized and configured to slidably engage a spline ring 118 on an inner surface of cover 102. Friction clutch plate 114 has a plurality of inner teeth 119 (only one labeled) that are sized and configured to slidably engage a damper assembly (not illustrated) coupled to a transmission (also not illustrated). As is known in the art, torque converter 100 provides a fluid coupling between an engine output shaft and a vehicle transmission that transmits torque from the engine to the transmission while allowing for different rotational speeds of the engine and transmission. As is also known in the art, lock-up clutch assembly 104 can be engaged to mechanically lock the engine and transmission at the same rotational speed under certain conditions in order to improve efficiency. When lock-up clutch assembly 104 is not engaged, cover 102, piston 106, metal clutch plates 112, and backing ring 110 rotate with the engine output shaft, while friction clutch plate 114 rotates at a different speed with the transmission. When lock-up clutch assembly 104 is engaged, piston 106 forces clutch plates 112, 114 together and against backing ring 110, thereby engaging clutch pack 108 and forcing friction clutch plate 114 and the transmission to rotate at substantially the same speed as cover 102 and the vehicle engine output shaft.
FIG. 2 is a cross sectional view of a portion of OE torque converter 100 showing piston 106 in a fully retracted position, resulting in a clutch release clearance 202 between the piston and a front side 204 of metal clutch plate 112F. An inner surface 205 of cover 102 and piston 106 define a piston apply chamber 206 for receiving pressurized transmission fluid for applying the piston against clutch pack 108 and backing ring 110. OE torque converter 100 is sometimes referred to as a “three-pass” torque converter because it includes three fluid ports (not illustrated)—two ports (inlet and outlet) for the passage of transmission fluid into and out of a main torus volume 208 of the torque converter, and a third port (also not illustrated) for delivering pressurized fluid to piston apply chamber 206. A transmission incorporating OE torque converter 100 typically includes a dedicated apply control circuit for controlling the pressure in piston apply chamber 206 and applying and releasing piston 106, which can provide a more responsive lock-up clutch assembly 104 apply and release than torque converters that do not have a dedicated piston apply control circuit.
Backing ring 110 is welded at weld B1 to cover 102. When OE torque converter 100 is repaired, backing ring 110 is typically removed to inspect or replace clutch plates 112, 114. When backing ring 110 is reattached after repairs are complete, clutch release clearance 202 must be maintained to ensure proper clutch operation. In this example, clutch release clearance 202 should typically be between 0.010-0.040 inches. It is, however, difficult to properly reattach backing ring 110 because it is difficult to hold and weld backing ring 110 in place with acceptable accuracy. It is also challenging due to the relatively short engagement C1 of backing ring 110 to cover 102 and because torque converter rebuilders lack the special fixtures and equipment that were used by the original equipment manufacturer (OEM) during original manufacture. As a result of these challenges, many aftermarket torque converter rebuilders are reluctant or refuse to rebuild this type of torque converter.
FIGS. 3 and 4 are close-up views of a portion of clutch pack 108, cover 102, and spline ring 118 showing the loose fit between teeth 116 of OE metal clutch plates 112 and OE spline ring 118. Example OE spline ring 118 is rolled formed and is sometimes referred to in the art as a “Grob spline” because it is manufactured by a cold forming process by proprietary machines made by ERNST GROB AG. Spline ring 118 is pressed into and attached by welding to an inside surface 302 of cover 102. Spline ring 118 is an OE low-cost construction and is not precise in form, resulting in a loose fit with the mating teeth 116 of metal clutch plates 112, the loose fit identified as D1 in FIG. 3. The loose fit also results in a minimal engagement length, indicated by E1 in FIG. 3, resulting in minimal contact area between teeth 116 and corresponding recesses 304 defined by spline ring 118.
FIG. 4 shows a leaf spring 402, which is included in OE torque converter 100 in part to account for the loose fit described above between spline ring 118 and metal clutch plate teeth 116. FIG. 4 shows both metal clutch plates 112F, 112R and also shows inner teeth 119 of friction clutch plate 114 extending radially inward from an inner diameter 404 of metal clutch plates 112. Leaf spring 402 maintains a relative circumferential position of metal clutch plates 112F, R. Leaf spring 402 is attached to teeth 116 by pins 406 and thereby circumferentially separates the two clutch plates 112F, R and forces teeth 116 against radially-extending walls 408 of recesses 304 of spline ring 118. (As shown in FIG. 1, example torque converter 100 includes six leaf springs 402 spaced circumferentially around clutch pack 108). Leaf springs 402 can also aid in disengaging metal clutch plates 112 from friction clutch plate 114 when lock-up clutch assembly 104 is released. Leaf springs 402, however, are prone to early failure. When one or more of leaf springs 402 fail, the loose fit between spline 118 and metal clutch plate teeth 116 can result in spline backlash between spline ring 118 and metal clutch plates 112, causing vibration, rapid wear and noise when the clutch is not engaged and also causing damage to spline ring 118, which can result in the spline ring being worn beyond repair, which can leave no practical options to rebuild OE torque converter 100.